Wireless differential resonance frequency pressure sensor: Circuital model and prototype validation

This article presents a pressure sensor composed of a set of three Archimedean spiral inductors. One of them is below the other two concentric spirals, where the upper coils are over a flexible membrane. When external pressure is applied over the sensor, the membrane deforms and changes the distance between the lower spirals and the upper inside coil, the capacitance, and its resonance frequency. However, once the sensor is in contact with a conductive medium, a change in the effective permittivity surrounding the sensor takes place reshaping the resonant frequencies. To improve the sensor response, we introduce a reader resonator sensor system. We present the comparative response of the system as a prototype, an analytical model, and a finite element model (FEM). The prototype system is fabricated using a photolithographic process for the elements of the sensor over a polymethylsiloxane and glass substrate, while the reader is fabricated over a FR4 substrate. COMSOL Multiphysics is used for the FEM simulation of the system to evaluate its behavior. The analytical model involves the integration of techniques to obtain the effective permittivity for each element plane and a coupled magnetic resonance to represent the interaction of the parts. We obtain a correspondence between the resonances of the different elements, with a maximum displacement frequency of 240 MHz for the proposed model, and 80 MHz in the FEM case related to the implemented prototype. The accuracy of this model allows a fast analysis to improve the design of this type of topology without high computational processing.